1. Field of the Invention
The present invention relates to an Internet protocol (IP) handoff method, and more particularly, to a handoff method between mobile agents (MAs) with respect to mobile nodes (MNs) in an environment including a plurality of mobile agent platforms (MAPs).
2. Description of the Related Art
As a handoff for a mobile Internet protocol (IP) referring to a book “IP-based next-generation wireless networks” by Jyh-Cheng & Tao Zhang (John Wiley & Sons Inc., 2004), there are an Intra-subnet handoff, an Inter-subnet handoff, and Inter-router handoff. A case where a moving mobile node (MN) needs a new IP subnet address corresponds to the Inter-subnet handoff and the Inter-router handoff for changing a jurisdiction address region of a router. A case where an MN that moves to an adjacent cell is in a jurisdiction address region cell of the same router corresponds to the Intra-subnet handoff. In the Intra-subnet handoff, the same IP subnet address is used, so that an IP handoff does not occur. Namely, when the MN visits a region having a different IP address region in a mobile IP network, a foreign agent (FA) that operates as a virtual router in an external network gives the MN a care of address (CoA), the MN registers the CoA at a home agent (HA) through the FA, the HA encapsulates data transmitted from the MA to transmit the encapsulated data to the CoA, and FA solves the encapsulated data and to transmit the solved data to the MN. In this case, the FA operates as a default router of the MN for the data transmitted from the MN.
However, when a signal path and a data path for the handoff described above are used together, there is a problem in that head-of-line blocking between routers for managing the IP subnet occurs.
U.S. Pat. No. 7,031,709 B2 (Apr. 18, 2006) provides a geographical FA topology relation in a case where a number of network providers and various wired/wireless access networks exist. More specifically, a provider Z which possesses subscribers but not access networks can acquire a new CoA when a node moves from A region to B region, an FA of the B region requires a possible CoA through an FA of the A region, and a HA of the provide Z can form a topology and a Map for access networks which are different from each other based on a mobility history of a subscriber node, so that the node can predict a mobility path and a rapid handoff can be performed. This method has an advantage of in that the method can be applied even when a construction statue of the access network is not known. However, there are problems in that it takes time for the HA to collect and learn the history of the mobility of the MN, and a conventional method of acquiring a CoA when the MN moves has to be changed. In addition, requiring a CoA of another region through the FA of a region may have a danger of a malicious attack. Namely, an impossible CoA in the B region is transmitted to the HA through a FA in another A region, so that a possibility of occurrence of binding update and deny message between the HA and the FA of the B region is very high.
As discussed by the Internet Engineering Task Force (IETF), a regional registration method of employing a gateway foreign agent (GFA) which is disposed above the FAs having different address regions from each other and registering a CoA provided from the GFA for the MN is introduced. However, in a case where signal packets or the handoff and IP data packets of the MN are used together, the problem of head-of-line blocking which is a characteristic of an IP network still remains. In addition, the MN needs an operation of registering with not only the conventional HA but also the GFA when perceives existence of the GFA.
In order to compensate for the disadvantages, a method provided in United States Patent 2005/0114543 A1 (May 26, 2005) which can be applied to the MN that cannot perceive the existence of the GFA is introduced. In this method, when the MN requests a registration of the HA through the FA, the GFA is disposed between the FA and the HA, so that the GFA adds an IP address of the GFA to an extension field of a registration request message of the MN transmitted from the FA. When the MN moves from the FA of the A region to the FA of the B region and the MN is registered with the GFA in advance, the MN receives a response with respect to a registration confirmation in an operation of confirming the registration request. When the MN is not registered, a new visitor entry is generated and added to a visitor list in the GFA, and the IP address of the GFA is added to an extension field of the registration request message of the MN transmitted from the FA of the B region, thereby transmitting the registration request message to the HA of the MN. In this case, there is an advantage in that conventional operations pf registering the MN at the normal HA can be used. However, there is a problem in that the operations can be performed only when the HA, GFA, and FA can perceive and process existence of the address of the GFA in the extension field of the registration request message. In addition, when the MN is not registered, the new visitor entry generated and added to the visitor list in the GFA before receiving a response with respect to the registration request from the HA have to be deleted when a deny message of a binding update is received. When the response with respect to the registration request message from the HA is late and in the meanwhile the MN moves to an FA of another region and requests a registration, since the GFA already exists in the visitor list, there is a possibility of information transmission in a state where the registration is not performed practically, so that a weakness for a malicious call exists. In addition, since all of data packets always pass through the GFA, there is a problem of an increase in data transmission paths. In addition, in this method, a signal processing process for an IP handoff between a number of GFAs is not mentioned, so that when the MN moves to another GFA, the MN has to re-start an IP handoff registration request to the HA through the visited GFA.
A method provided in United States Patent 2004/0198383 A1 (Oct. 7, 2004) is to separate a paging foreign agent (PFA) for supporting paging of an MN from a controlling foreign agent (CFA) for controlling the PFA to form a hierarchical architecture in which the PFA is disposed below the CFA. In this method, the CFA and the PFA add their addresses to a fixed field inside an advertisement message extension to send the advertisement message extension to the MN, so that an IP handoff registration request of the MN can be performed. The method and operations provided therein are similar to an operation of requesting regional registration to the CFA by the MN in the regional registration method currently being discussed by the IETF. Therefore, when the signal packets for the handoff and IP data packets of the MN are used together, the problem of head-of-line blocking which is a characteristic of the IP network still remains. In addition, there is a problem in that the MN has to perceive existence of a GFA and request a registration of the GFA in addition to perform an operation of registering with the existing normal HA. In addition, operations performed when the MN moves from a CFA to another CFA are not mentioned, so that the MN has to re-start the IP handoff registration request of the HA through another visited CFA when the MN moves to another CFA.
United States Patent 2002/0143993 A1 (Oct. 3, 2002) is introduced to enable a mobile IP support in International Mobile Telecommunications-2000 (IMT-2000) employing an asynchronous method as in Europe. In consideration of the connection-oriented asynchronous method, a gateway general packet radio service (GPRS) support node (GGSN) constructed for IMT-2000 has functions of the FA and the GFA so as to selectively perform the function of the GFA, and a GPRS Tunneling Protocol (GTP) tunnel is guaranteed between the MN and the GGSN, so that the MN registers position information in the HA.[GPRA->GPRS] This method provides an advantage of applying the GFA method to an IMT-200 system in a European method. However, there are problems in that the MN has to include a function of perceiving existence of the GFA, all of the GGSNs have to include the GFA function, and a problem of the existing GFA method in that the GFA always broadcasts along a data path between the a correspondent Node (CN) and the MN and data transmission paths increase still remains. In addition, operations performed between a number of providers, that is, a number of GFAs are not mentioned.
United States Patent 2006/0018291 A1 (Jan. 26, 2006) employs a gateway router (GR) which has a similar concept and operation to that of the above GFA and a local mobility anchor (LMA) which as the same concept as the MA and provides a method in which, when the MN moves between the LMAs and the GR receives a CoA of the MN from a HA, data packets transmitted from a CN do not pass through the HA and are directly transmitted to the LMA at which the MN is disposed, so that packet paths reduce. In addition, in this method, the CoA of the MN is not transmitted to the CN, and a unit for protecting (hiding) a current position of the MN from the CN is provided. The method has a problem in that data of the CN always has to pass the GR. In addition, since data paths and signal packet transmission paths for a handoff (binding update, etc) are not separated from each other, when the same paths are used, the problem of head-of-line still remains. In addition, a case where a number of providers and a number of GRs exist is not mentioned. In addition, in order to apply the method in the existing Internet protocol version 6 (IPv4) not the IPv6, conventional operations of the HA have to be changed.